S.:
Congrats on your baby!!!
Hmmmm....soreness under the nipple? Is there a lump or hardness there? If so - it MIGHT be mastitis....
I would contact your PCP or your GYN to ask them if they want to see you or if they feel that you can put a warm wash cloth over it to help alleviate the pain.
The breast being larger? Happens - even when you are not nursing...my left is bigger than my right...and I've not nursed in 8 years!! :)
I would try pumping to see if you are getting all of the milk out - the hind milk can hang in there....
GREAT JOB MAMA!!!!